1. Technical Field
The present disclosure relates to electrosurgical instruments and, more particularly, to open or endoscopic electrosurgical instruments having compressible or elastomeric end effector assemblies for use in sealing various tissues.
2. Background
A hemostat or forceps is a simple plier-like tool which uses mechanical action between its jaws to constrict vessels and is commonly used in open surgical procedures to grasp, dissect and/or clamp tissue. Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal.
By utilizing an electrosurgical forceps, a surgeon can either cauterize, coagulate/desiccate and/or simply reduce or slow bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied through the jaw members to the tissue. The electrode of each jaw member is charged to a different electric potential such that when the jaw members grasp tissue, electrical energy can be selectively transferred through the tissue.
In order to seal large vessels, two predominant mechanical parameters must be accurately controlled—the pressure applied to the vessel and the gap distance between the electrodes—both of which are affected by the thickness of the sealed vessel to be sealed. More particularly, accurate application of pressure is important to oppose the walls of the vessel; to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue; to overcome the forces of expansion during tissue heating; and to contribute to the end tissue thickness which is an indication of a good seal. It has been determined that a typical fused vessel wall is optimum between 0.001 and 0.005 inches. Below this range, the seal may shred or tear and above this range the opposing tissue layers may not be properly or effectively sealed.
With respect to smaller vessels, the pressure applied to the tissue tends to become less relevant whereas the gap distance between the electrically conductive surfaces becomes more significant for effective sealing. With smaller vessels, the chances of the two opposed electrically conductive surfaces of the electrosurgical forceps touching during activation increases as the size of the vessel becomes smaller.
The process of coagulating small vessels is fundamentally different than electrosurgical vessel sealing. For the purposes herein, “coagulation” is defined herein as a process of desiccating tissue wherein the tissue cells are ruptured and dried. “Vessel sealing” meanwhile is defined herein as a process of liquefying the collagen elastin and ground substances in the tissue so that it reforms into a cohesive, fused mass. Coagulation of small vessels is sufficient to permanently close the vessel lumen. Larger vessels need to be sealed to assure permanent closure.
U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and 4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and 5,312,433 to Boebel et al., U.S. Pat. Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No. 5,951,549 to Richardson et al., all relate to electrosurgical instruments for coagulating, cutting and/or sealing vessels or tissue. However, some of these designs may not provide uniformly reproducible pressure to the opposing tissue layers which in turn may result in an ineffective or non-uniform seal. For example and with particular respect to variously-sized tissues, many of these references disclose instruments which unevenly compress the tissue across the jaw surface which is not conducive to consistent or effective tissue sealing.
Many of these instruments rely on clamping pressure alone to procure proper sealing thickness and are not designed to take into account gap tolerances and/or parallelism and flatness requirements which are parameters which, if properly controlled, can assure a consistent and effective tissue seal. For example, it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of many reasons: 1) if tissue is initially thin or if too much force is applied, there is a possibility that the two electrically conductive surfaces of the instrument will touch and energy will not be transferred through the tissue resulting in an ineffective seal; 2) if tissue is thick or too low a force is applied, the tissue may pre-maturely move prior to activation and sealing and a thicker, less reliable seal may be created; or 3) if the tissue is thick, over compression may lead to tissue vaporization and a less reliable seal may be created.
Moreover, the performance of certain existing clamping RF delivery systems is limited due to their inherent tendency to arc and short once the directly opposing electrodes have been drawn into close proximity with one another. Maintaining a functional and reliable system with a directly opposed configuration requires tight tolerances on specific parameters such as electrode gap and jaw parallelism.
Thus, a need exists to develop an electrosurgical instrument which effectively and consistently seals variously-sized tissue and solves many of the aforementioned problems known in the art.